/Engine/Source/Runtime/Engine/Public/Elements/SMInstance/SMInstanceElementId.h
Delegate called when a static mesh instance is about to be removed from the instances array on its component, and the associated ID for a SMInstance element will be unmapped.
typedef TMulticastDelegate_TwoParams< void, const [FSMInstanceElementId](API\Runtime\Engine\Elements\SMInstance\FSMInstanceElementId) &, int32 > FOnInstancePreRemoval